1. Field of the Invention
The present invention relates to a starting device for an electric starter motor (self starter motor) which is used as an apparatus of starting an engine, particularly, a small-sized engine.
2. Description of the Related Art
Conventionally, there has widely been known a self-motor of this kind illustrated in FIG. 19 of JP-A-2-108855. According to the self-motor disclosed in the publication, a fly wheel integrally formed with a cooing fan is attached to a crank shaft projected from an engine main body. A ring gear is attached to the outer periphery of the fly wheel. A starter motor having a length the same as a width of the engine main body is attached to a side face portion of the engine main body. A drive gear is fixed to an outer peripheral face of a drive shaft projected from the starter motor. Further, when the starter motor is driven, the drive shaft is projected out and the drive gear is brought in mesh with the ring gear to thereby rotate the crank shaft via the fly wheel. A clutch structure is constituted such that when the engine is brought into a started state in this way, the drive shaft of the starter motor is drawn to an original state and the engagement of the drive gear with the ring gear is disengaged.
As described above, according to the conventional self-motor, the engine needs to start by bringing the drive gear in mesh with the ring gear installed at the outer periphery of the fly wheel having a large diameter. Therefore, a starter motor of a style which is large-sized and is provided with large drive force is obliged to use and its fabrication cost is expensive. Further, there is constructed the constitution in which the drive gear of the drive shaft is brought in mesh with the ring gear installed at the outer periphery of the fly wheel. Therefore, there causes an inconvenience in which a dimension of a total of the engine in the diameter direction is significantly magnified since the starter motor is arranged to attach to the side face portion of the engine main body.
In order to resolve such an inconvenience, the applicant has proposed a starting device for an electric starter motor comprising a ring gear driven by two or more of small-sized motors and a clutch mechanism installed between the ring gear and an engine for starting the engine by rotating the ring gear in Japanese Patent Application No. 73381/1998.
Although the proposed starting device for an electric starter motor is effective in resolving the above-described inconvenience, there is constructed a constitution in which pairs of ring gears and motor side gears are brought in mesh with each other in parallel and accordingly, the diameter of the ring gear is obliged to magnify. Accordingly, a total of the engine integrated with the starting device cannot be expected to downsize significantly and the torque of the small-sized motor needs to increase.
Further, even when a reduction gear is interposed therebetween such that large torque is not needed in the small-sized motor, a large-sized reduction gear cannot be arranged since dimensions in a radial direction and an axial direction are restricted in view of an attachment pitch of a starter case, incorporated parts and so on.